Recent years have found wide application of pouch containers made of plastic film and formed into a bag shape by sealing, for packaging various liquid contents including hygiene products such as detergent and shampoo, and food products or seasoning such as soy source. Pouch containers are also widely used as refill pouches whose contents are transferred to other containers such as plastic or glass bottles.
Such pouch containers are produced, for example, as shown in Patent Document 1 specified below, by continuously feeding superposed upper and lower webs of plastic film with plastic bottom material interposed between the two webs at both lateral edges, sealing both lateral edges in the feed direction and crossing portions extending in the width direction and spaced apart at predetermined intervals, and successively cutting the webs at the center in the width direction and at the centers of the respective crossing portions.
The cut section at the center in the width direction forms the upper end opening of each pouch container, and after the pouch is filled with the content from this opening, the opening is tightly sealed.
One known bag making apparatus for continuously mass-producing such pouch containers includes, for example, as shown in Patent Document 2 specified below, a continuous feed mechanism for continuously unwinding a rolled web of film and feeding the web of film at a predetermined speed, an intermittent feed mechanism for intermittently feeding the web of film by a predetermined amount, a feed adjustment mechanism provided between the continuous feed mechanism and the intermittent feed mechanism (shown as “accumulators 7 and 8” in Patent Document 2), and a sealing mechanism for sealing predetermined portions of at least two, upper and lower, webs of film fed by the intermittent feed mechanism.
The feed adjustment mechanism (“accumulators 7 and 8”) of this known bag making apparatus is provided for absorbing slack in the web of film caused by periodic fluctuations in the feed amount between the continuous feed and the intermittent feed, and for reducing tension fluctuations. The web of film passes over a movable dancer roll, and tension applied to the moving dancer roll is made constant so as to absorb slack in the web of film between the continuous feed and the intermittent feed as well as to absorb tension fluctuations at the same time.
The feed amount for the intermittent feed is set to match the size of one pouch container, and one portion is sealed through several stages by a plurality of sealing unit aligned at an equal distance. Since the web of film stretches due to the tension at this time, the feed amount corresponding to one bag needs to be adjusted.
The apparatus is therefore configured to determine a portion to be sealed based on a mark provided on a printed surface of the web of plastic film. The mark is imaged by a CCD camera to determine its position and to detect any displacement in the position of the mark during the intermittent feed, based on which the intermittent feed amount and the spacing between the plurality of sealing unit are adjusted.
In such a bag making apparatus for producing pouch containers including a continuous feed mechanism for continuously unwinding a rolled web of film and feeding the web of film at a predetermined speed, an intermittent feed mechanism for intermittently feeding the web of film by a predetermined amount, a feed adjustment mechanism provided between the continuous feed mechanism and the intermittent feed mechanism, and a sealing mechanism for sealing predetermined portions of at least two, upper and lower, webs of film fed by the intermittent feed mechanism, in order to produce high-quality pouch containers without any displacement of the print, it is important to precisely set the position and feed amount of the intermittent feed, to reduce tension fluctuations, and to prevent wandering and skewing of the web of film, as much as possible.
Patent Document 1: Japanese Patent Application Laid-open No. 2007-168147
Patent Document 2: Japanese Patent Application Laid-open No. 2003-33981
Patent Document 3: Japanese Patent Application Laid-open No. H8-217020
The known bag making apparatus is configured to absorb slack in the web of film caused by periodic fluctuations in the feed amount between the continuous feed and the intermittent feed, and to absorb tension fluctuations at the same time, by unit of a dancer roll. The moment of inertia when the moving direction of the dancer roll is changed would sometimes not only reduce the effect of absorbing tension fluctuations but also work contrarily and cause variations in tension.
In order to keep such tension fluctuations caused by the moment of inertia within a practically tolerable range, the moving speed of the dancer roll has to be kept low. As the web of film cannot be fed at higher speed, this was a hindrance to higher productivity.
Another possible solution would be to provide a plurality of dancer rolls for the web of film to travel over, to reduce the moving speed of the dancer rolls and to reduce the influence of the moment of inertia when the moving direction is changed. However, this is not a fundamental solution, because the influence of the rotational moment of inertia when the rotation speed of the dancer rolls is changed, and of friction, is increased, contrarily.
Further, vibration of other movable elements would sometimes cause variations in tension.
To alleviate these problems, an apparatus is known, as shown in Patent Document 3 specified above, wherein a dancer roll for absorbing slack in the web of film is forcibly driven at a predetermined speed and in a predetermined range, while another dancer roll is provided for absorbing tension fluctuations, so that tension fluctuations are absorbed without increasing the number of dancer rolls.
However, although the amount of movement of the dancer roll assigned for absorbing the tension fluctuations is reduced, the problem associated with its reciprocal movement remains, and the influence of the rotational moment of inertia when the rotation speed is changed, and of friction, is inevitably increased as there is one more dancer roll. Thus, while tension fluctuations may be somewhat reduced, the feed speed of the web of film could be increased only to a limited extent.
Another problem is that the tension applied on the web of film causes the web to stretch, and tension fluctuations during continuous production cause variations in the elongation of the web of film, because of which, with the initial settings of the intermittent feed amount in the intermittent feed mechanism and the spacing between the plurality of sealing unit in the sealing mechanism that are based on the values of elongation assumed at the start of production, the position to be sealed may be displaced from a desired position.
For this reason, marks provided on the printed surface have to be imaged with a CCD camera to detect their positions for monitoring purposes during the continuous production, and when any displacement is detected, the intermittent feed amount and the spacing between the plurality of sealing unit have to be adjusted, which require extra time. The detection and adjustment may be automated, which would, however, require a complex configuration and make it harder to increase the feed speed of the web of film. Thus this was another hindrance to better production efficiency.
The reciprocal movement and changes in the rotation speed of dancer rolls would not only cause tension fluctuations but also vibration in the entire apparatus or the web of film, or cause the web of film to flutter up and down. Such vibration and fluttering are one cause of skewing of the web of film. The larger the tension fluctuations, or the action of the mechanism for absorbing tension fluctuations, the more irregularly and significantly the web would wander or skew, because of which the mechanism for correcting a bend or skew would inevitably have a complex and bulky structure.